1. Field of the Invention
The present invention relates to an optical pickup device that is capable of reading signals from an optical recording medium such as an optical disc or recording signals to the optical disc, and, more particularly, to an optical pickup device including a plurality of object lenses.
2. Related Art
Generally, an optical pickup device for use in an optical recording and/or reproducing apparatus is a device that irradiates a laser beam on an optical disc, such as a compact disc (CD) or a digital video disc (DVD), to read information from the optical disc or to record information on the optical disc. The optical pickup device includes a drive unit to drive an object lens in a radial direction of the optical disc to seek a track of the optical disc and to drive the object lens in the direction of an optical axis to control focus of the laser beam, when the laser beam irradiated on a recording layer of the optical disc is out of focus.
An example of such an optical pickup device is disclosed in Japanese Unexamined Patent Publication No. 2003-109234. The disclosed optical pickup device changes the position of an object lens to adjust the position where a laser beam is irradiated onto an optical disc. The optical pickup device includes focus coils symmetrically mounted at opposite sides of a bobbin and tracking coils symmetrically mounted at opposite sides of the focus coils. The focus coils and the tracking coils are disposed in a symmetrical fashion such that the weight balance is maintained. According to the disclosed optical pickup device, deviation in weight is eliminated, and, as a result, a drive force generated by coils is uniformly applied in all directions to accurately and easily perform focus correction of the laser beam. The disclosed optical pickup device is one form of optical pickup devices having a single object lens.
Recently, there has been increasingly a requirement for an optical pickup device that is capable of recording/reproducing information on/from various kinds of optical discs having different recording densities, such as compact disc (CD), a digital video disc (DVD), or a blu-ray disc (BD).
It is required, however, that such an optical pickup device have a plurality of object lenses corresponding to various kinds of optical discs, a plurality of optical paths be formed for the respective object lenses, and focus coils and tracking coils to correct focus of the laser beam be balanced. As a result, the structure of the optical pickup device is complicated, the manufacture of the optical pickup device is difficult and cost prohibitive, and the miniaturization of the optical pickup device is difficult and prone to inaccuracy.